The Environmental Protection Agency now says there is “mounting evidence” that Monsanto’s genetically modified corn is losing its ability to resist insect infestations such as the Western rootworm, despite increased applications of pesticides.

The EPA’s comment came in response to questions arising about a recent study that observed Western rootworms that had developed resistance to the genetically modified Monsanto corn and its companion pesticide, the glyphosate-based Roundup, on two Illinois farms.

Rootworms damage crops by preventing the plants from pulling water and nutrients from the soil. They caused about $1 billion a year in crop damages before Monsanto and other biotech companies developed insecticide expressing genetically modified corn crops designed to reduce the amount of infestations and reduce damages and losses for farmers.

Genetically modified crops like Monsanto’s soy, corn and cotton, provided farmers a few years worth of pest-free yields before the rootworms and ‘superweeds‘ started showing an ability to withstand excessive pesticide use and resist the crops that express pesticides through their genes (Bt). Swiss biotech giant, Syngenta, says that as many as 28 million acres of GMO soy, corn and cotton may be home to Roundup resistant pests by 2015, which could create record high crop losses. With extreme droughts currently plaguing U.S. farmland, losing more crops to infestations could mean severe devastation for farmers, driving up food and fuel prices as a result.

Despite the studies and acknowledgment of the issue by the EPA, Monsanto spokesperson Kelly J. Clauss said in an email to Bloomberg Businessweek that the studies conducted in Illinois and Iowa do not confirm widespread resistance, adding that more data is needed in order to prove there is an issue. Monsanto says it is working with the EPA to “investigate and respond to fields where rootworms cause “greater-than-expected damage.”